1. Field of the Invention
This invention relates generally to implantable medical devices, and, more particularly, to methods, apparatus, and systems for using feedback data from a medical imaging system to affect an operation performed by an implantable medical device (IMD).
2. Description of the Related Art
There have been many improvements over the last several decades in medical treatments for disorders of the nervous system, such as epilepsy and other motor disorders, and abnormal neural discharge disorders. One of the more recently available treatments involves the application of an electrical signal to reduce various symptoms or effects caused by such neural disorders. For example, electrical signals have been successfully applied at strategic locations in the human body to provide various benefits, including reducing occurrences of seizures and/or improving or ameliorating other conditions. Examples of such a treatment regimen involve applying an electrical signal to the vagus nerve of the human body to reduce or eliminate epileptic seizures, as described in U.S. Pat. Nos. 4,702,254, 4,867,164, and 5,025,807 to Dr. Jacob Zabara, and the treatment of neuropsychiatric disorders such as depression, as described in U.S. Pat. No. 5,299,569 to Joachim Wemicke et al. The foregoing patents are hereby incorporated in their entirety herein by reference in this specification. Electrical stimulation of cranial nerves, such as the vagus nerve (hereinafter referred to as vagus nerve stimulation therapy or VNS) may be provided by implanting an electrical device underneath the skin of a patient and performing a detection and electrical stimulation process. This type of stimulation is generally referred to as “active,” “feedback,” or “triggered” stimulation. Alternatively, the system may operate without a detection system once the patient has been diagnosed with a disorder treatable by cranial nerve stimulation (such as epilepsy or depression), and may periodically apply a series of electrical pulses to the cranial nerve intermittently throughout the day, or over another predetermined time interval. This type of stimulation is generally referred to as “passive,” “non-feedback,” or “prophylactic,” stimulation. An implantable medical device that is implanted within the patient's body may apply the stimulation.
State-of-the-art implantable medical devices generally deliver stimulation signals to one or more regions of a patient's body in a predetermined periodic cycle. Based upon the diagnosed disorder of the patient, a physician may determine a regimen of therapeutic stimulation signals to treat the disorder. The devices then execute the predetermined therapy regimen. This regimen may be interrupted by predetermined interruption protocols, such as an external communication from a physician prompting a change in the regimen, a signal from the patient, etc.
As used herein, “stimulation” refers to the application of an electrical, mechanical, and/or chemical signal to a neural structure in the patient's body. In one embodiment, the stimulation comprises an electrical signal. The stimulation signal may induce afferent and/or efferent action potentials on the nerve, may block native afferent and/or efferent action potentials, or may be applied at a sub-threshold level that neither generates action potentials nor blocks native action potentials. In some embodiments, the stimulation signal is a signal that is capable of inducing afferent and/or efferent action potentials on the nerve.
The stimulation signal applied to the neural structure in embodiments of the present invention refers to an exogenous signal that is distinct from the endogenous electrical, mechanical, and chemical activity (e.g., afferent and/or efferent electrical action potentials) generated by the patient's body and environment. In other words, the stimulation signal (whether electrical, mechanical or chemical in nature) applied to the nerve in the present invention is a signal applied from an artificial source, e.g., a neurostimulator.
Providing an electrical signal for stimulation of a cranial nerve may cause variations in the electrical activity of portions of a patient's brain. However, state-of-the-art IMDs generally do not allow for affecting the predetermined stimulation regimens in response to these physiological brain variations. Barring active initiation of operational changes prompted by an external source, such as a physician, state-of-the-art implantable medical devices generally continue a predetermined treatment regimen despite the physiological variations in the brain. This may cause the implantable medical device to become less accurate in targeting specific regions of the brain for treating specific disorders. Further, state-of-the-art medical systems generally do not have sufficient feedback as to the effectiveness of the stimulation in terms of targeting certain regions of the brain.
Generally, state-of-the-art electrical IMDs may cause a reaction in a patient's brain by stimulation of cranial nerves. The effects of the stimulation are evaluated on a long-term basis, where physicians may evaluate whether sufficient improvement relating to the disorder has taken place over time. However, this methodology generally lacks the ability to perform more short-term adjustments. In other words, the time period between delivering stimulation and studying the effects of the stimulation is substantially long—typically months or even exceeding a year. Therefore, a substantial amount of time may elapse to determine whether a stimulation regimen has improved the treatment or condition. Thus, finding the appropriate stimulation regimen can be delayed substantially due to the state-of-the-art methodologies.
In an attempt to alleviate some of these problems, designers have provided for altering the regimen based on an external input or input from the patient, for example, through a magnetic signal sent to the implantable medical device. However, this solution may not be sufficiently reactive to adequately address variations in the brain resulting from particular stimulation regimens. For example, a patient is generally unable to determine the effects of the stimulation to certain portions of the brain. Further, these solutions may require an assessment by an external source, such as a physician or the patient. By the time an external source examines the physiological variations produced by the stimulation, the patient's brain may have undergone further changes, rendering any reaction to the original physiological variations obsolete.
Even though delivery of stimulation signals may cause specific physiological variations in the patient's brain, state-of-the-art implantable medical devices generally behave independently of such variations, at least in the short term. Long-term changes may be provided by re-examination by a physician, i.e. re-diagnosis of a disorder, and then making further adjustments to the stimulation treatment. This may result in significant delay between the physiological changes that may occur due to stimulation, and the time when a physician makes manual adjustments to the stimulation regimen after examination. Therefore, efficient and effective reaction to physiological changes may not take place utilizing state-of-the-art implantable medical devices. Further, targeted regions of the brain may not be adequately affected by a particular stimulation regime, possibly leading to reduced treatment efficacy.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.